Improvement of convergence property in the PSS parameter optimization under multiple system operating conditions

The objective function of the nonlinear programming method, used to optimize power system stabilizer(PSS) parameters under multiple operating conditions in a multi-machine system, is modified to improve the convergence property. The improved objective function is composed of the real part of all unstable and some stable eigenvalues, together with damping ratios of all eigenvalues dissatisfied and some eigenvalues satisfied with the system dynamic quality. These considered eigenvalues are multiplied by weighting coefficients determined by their corresponding stabilization degree. Based on an eight-machine system, convergence properties of the quasi-Newton method used to solve the optimization problem are discussed in details, with different eigenvalue range values and several weighting coefficient expressions, including the inverse function, linear function and so on. From these testing computations, both the weighting coefficient selecting rules and the preferable eigenvalue range are concluded. The results show that the convergence property can be improved efficiently by the proposed approach.Department of Electrical Engineerin